Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Wakefield Virginia
945 PM EDT Wed Mar 29 2017
high pressure becomes centered off the northeast coast tonight and
Thursday. Low pressure and associated frontal boundaries track
across the region Friday. High pressure builds over the area for the
Near term /until 6 am Thursday morning/...
current WV imagery shows a potent low over the Central Plains,
with an upper ridge extending nwd from the southeast conus
through the Ohio Valley and ern Great Lakes. At the surface,
high pressure is centered over James Bay, and will build into
the mid-Atlantic from the north this evening and will continue
expand swd overnight, with a light east-northeast wind developing. Mostly
clear this evening, with increasing clouds after midnight,
primarily across the Piedmont. Cooler tonight with lows ranging
from the upper 30s/around 40 north/NE, to the low/mid 40s S.
Short term /6 am Thursday morning through Saturday/...
500 mb ridge becomes centered off the coast Thursday. Tsctns show
moisture at various levels due to warm air advection atop the stable onshore flow.
Expect partly cloudy skies east, mstly cloudy to cloudy west with
any upslope shwr activity remaining west of the fa. Given weak/low
mixing and the cloud coverage, expect a cooler day with highs 55-60
except 50-55 at the beaches.
Moisture increases late Thursday night ahead of approaching upr
level low. Will keep the evening dry with shwrs overspreading the
area after midnight. Pops range from chc along the coast to likely
across the Piedmont. Lows in the low-mid 40s.
Rather challenging forecast Friday as the models continue to prog a
strong closed low to become negatively tilted as it crosses the
region. Main sfc low to track north of the fa but data suggests
another spoke of energy will rotate arnd the main low resulting in a
triple point low crossing northern Virginia Friday afternoon and evening
before moving off the New Jersey coast Friday night. Copious amounts of
Atlantic moisture forecasted ahead of the low along with pw's btwn
1.25 to 1.50 inches. This will lead to locally heavy downpours
Friday. Challenge for the afternoon will be the amount of convection
that develops. Storm Prediction Center has the southern half of the fa in a marginal
risk but a lot of uncertainty remains on just how unstable it
becomes. Thus, categorical probability of precipitation will be maintained across the fa
with thunder chcs limited to the afternoon and mainly across
the south. Slght chc thunder across the north. Temps tricky and
may depend on any heating that occurs. Highs in the 60s except
near 70 southern most zones.
Likely to categorical probability of precipitation continue Friday evening with probability of precipitation
tapering off after midnight as the low pulls offshore. Thunder chcs
will be limited to the evening and mainly across the south and
east. Lows in the upr 40s-mid 50s.
Trailing upr level energy tracks across the Eastern Shore early Sat.
Will keep slght chc morning pops there, otw decreasing cldns. Highs
in the low-mid 60s Eastern Shore, mid 60s-lwr 70s west of the Bay.
Long term /Saturday night through Wednesday/...
weak high pressure returns to the region Sat night/sun with
northwest flow aloft. Mostly clear skies and cool temperatures
anticipated with lows in the 40s Sat night and highs in the 60s
sun (upper 50s Atlantic beaches). High pressure slides offshore
Sun night/Mon as the next low pressure system deepens over the
arklatex region/lower Mississippi Valley. The low continues to
track NE into nrn Ohio/PA Mon night into Tue...dragging a cold
front through the mid Atlantic region Tue aftn/evening. Increasing
cloudiness late Sun night into Mon with similar temps to sun. Lows
in the 40s Sun night, and highs in the 60s Mon (upper 50s Atlantic
beaches). Sfc pressure gradient tightens substantially late Mon
night into Tue ahead of the approaching cold front. S-west winds
gusting up to 25-30 mph will be possible. Widespread rainfall is
anticipated during this timeframe with very low thunderstorm
chances due to rain occurring primarily in the morning. Warmer
temperatures Mon night/Tue as a warm front lifts north through the
region. Lows Mon night in the mid-upper 40s far nrn counties (i.E.
North of the warm front) and in the lower 50s elsewhere. Highs
Tue in the 60s far nrn counties and in the lower 70s elsewhere.
Aviation /02z Thursday through Monday/...
VFR conditions prevail over the region as high pressure over
the region moves east overnight. Strong low pressure over the
southern Great Plains will move northeast into the Ohio Valley
Thursday allowing mid and high clouds to increase over the mid
Atlantic region. Winds will be from the north-NE 5 to 10 kt tonight
and will shift east-southeast on Thursday 10-15 kt.
Outlook...low pressure will move from the Ohio Valley across
northern portions of the mid Atlantic states to south of New
England by Saturday morning. Widespread rain develops Friday
morning with a chance for thunderstorms Friday afternoon and
evening. Periods of MVFR/IFR will be likely. Conditions improve
by Saturday morning. High pressure builds back into the area for
the weekend. There will be a chance for showers western
portions of the area by late Monday as the next system develops
over the Mississippi Valley.
high pressure continues to build into the region from the north
tonight and slides across the Delmarva on Thu. Breezy north-northeast winds
10-15kt through early evening will diminish around sunset. Although
a diurnal increase in winds is anticipated late tonight into Thu
morning, persistent onshore/NE-E winds will remain aob 15kt through
Thu. However, seas could reach up to 5ft out near 20nm in north-northeast swell
and have issued Small Craft Advisory flags for all coastal waters from 500am through
700pm thu; may be able to drop headlines with forecast package late
High pressure slides offshore Thu night as an approaching low
pressure system tracks over the Great Lakes states. Winds become
more southeast overnight. Speeds still aob 15kt with seas 3-4ft/waves 2ft.
The sfc pressure gradient tightens on Fri as a warm front lifts north
across the area Fri morning ahead of an approaching cold front, which
is expected to cross the waters Fri evening. Wind speeds are expected
to increase to low-end Small Craft Advisory (15-25kt) Fri morning...becoming SW-west and
decreasing aob 15kt Fri evening with the cold frontal passage. Seas
also build to 5ft Fri morning and could reach up to 6ft nrn coastal
waters Fri aftn...primarily due to onshore swell. Elevated seas around
5ft expected through Fri night...possibly lasting through sun for far
nrn coastal waters. Waves on ches Bay should average 2-3ft on Fri.
Weak high pressure returns to the region Sat/sun with northerly winds
aob 15kt Sat and aob 10kt sun. Seas 3-5ft far nrn coastal waters/2-4ft
srn coastal waters. Waves generally 1-2ft.
Marine...Small Craft Advisory from 5 am to 7 PM EDT Thursday for anz650-